As shown in FIGS. 3 and 4, a conventional terminal block includes, for example, a block body 4 for forming a space for insertion of a wire end 100 which is a conductive portion of the wire, and a clamping portion 30 for clamping the wire end 100 inserted into the space against a clamping surface 4c which is an inner bottom surface of the block body 4.
Clamping portion 30 includes a screw 31 provided with a screw head 31a and a screw shank 31b, and a clamping plate member 33 clamping wire end 100 between clamping surface 4c with a pressure developed by turning of screw 31. Clamping plate member 33 is joined to a lower end of screw shank 31b so that clamping plate 33 is moved vertically in accordance with an axial movement of screw 31.
The block body 4 is formed, for example, by bending an elongated metal plate member at right angles at four positions in the same direction and superposing the first flap 4a and the last flap 4b. Flaps 4a and 4b are provided with threaded bores each with a thread matching the thread of screw shank 31b. Flaps 4a, 4b are disposed to overlap each other so that centers of these threaded bores coincide when a wire end 100 is not clamped.
In the conventional terminal block with the configuration mentioned above, a wire end 100 inserted between the clamping plate member 33 and the clamping plate 4c is clamped by tightening the screw 31. The terminal block is able to establish an electrical connection with the electrical wire through the conductive portion of the clamped wire end 100, by constructing one of the clamping plate member 33 or the clamping surface 4c from a conductive material.
As the screw 31 is tightened further, flaps 4a, 4b of the block body 4, in which the threaded bores are formed, start to open outwards. Flaps 4a, 4b develop spring elastic forces since the block body 4 is composed of metal. These elastic forces are utilized to press the screw 31 downward constantly so as to prevent the screw 31 from being loosened.
However, the mechanism for preventing the screw 31 from being loosened in the conventional terminal body is not effective enough in some cases. For example, the loosening of the screw 31 may not be sufficiently prevented, depending on the strength of mechanical vibrations applied to the terminal block. In such a case, the clamping force on a wire end 100 may not be strong enough, and in the worst case the wire end 100 may come away from the terminal block.